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Coral bleaching lifeboat could be just beneath the surface (University of the Ryukyus)

A report commissioned by the United Nations offers a glimmer of hope to those managing the impact of bleaching on the world’s coral reefs. 

This year has seen several massive bleaching events on some of the most diverse corals reefs of the planet, including the Great Barrier Reef, a result of the continuing rise in global temperatures and exacerbated by this year’s major El Niño event. With the arrival of the summer in Japan, it is not yet known if bleaching events will also affect Japanese coral reefs, but researchers are already preparing for such eventuality.

The 35 authors of the United Nations Environmental Programme – including Dr Frederic Sinniger from the University of the Ryukyus Tropical Biosphere Research Center - say as the world's surface reefs are being threatened, part of the ecosystem may survive in these barely known deeper environments, known as mesophotic coral ecosystems (MCEs).

Upper mesophotic corals in Okinawa, Japan, 40 m depth. Among other corals, this picture shows the branching Seriatopora hystrix; a coral highly sensitive to bleaching who disappeared from the nearby shallow reefs following massive bleaching events but is still abundant at mesophotic depths. (Photo: F. Sinniger)

Shallow coral reefs from the water’s surface to 30-40 metres depth are the tip of the iceberg that comprises the ocean’s extensive coral ecosystem. MCEs are intermediate depth reefs starting at about 40 metres depth and continuing to around 150 metres. Too deep for most SCUBA divers, too shallow for most submersibles and deep-sea research vessels, MCEs are part of the few remaining places on earth that are largely unexplored. The report – ‘Mesophotic Coral Ecosystems A lifeboat for coral reefs?– looks at the role MCEs could play in the preservation of shallower reefs.

If MCEs are more protected from extreme environmental conditions such as high sea surface temperatures, the report asks if MCEs can provide a refuge for the species under threat in shallower reef ecosystems and whether they can provide the stock to re-populate shallow reefs if they continue to decline. “Mesophotic coral ecosystems are a seed bank for some organisms,” said one of the lead authors, Professor Baker from the University of Sydney, Australia. In addition to this role, organisms living in MCE may have additional value for our society. “Each biodiversity survey in MCEs discovers species new to science.” said Dr. Sinniger from the University of the Ryukyus.

The review brought together for the first time information on the geology, biology, distribution, biodiversity and socio-economic aspects of mesophotic reefs in order to examine their potential resilience. It found some deep mesophotic coral ecosystems may be less vulnerable to the most extreme ocean warming, but others may be just as vulnerable as their shallow counterparts and cannot be relied on to act as “life boats”.

The report’s recommendations include:

  • Locate where mesophotic reefs exist.
  • Increase our understanding of how they are connected to shallow reefs.
  • Raise awareness amongst managers and policy makers of the potential importance of MCEs.
  • Expand reef monitoring programmes to include MCE habitats.

This report will be launched on the 24th of May during the United Nations Environment Assembly (UNEA) in Nairobi, Kenya.

For further info, contact:

Frederic Sinniger Harii, PhD, Tropical Biosphere Research Center, University of the Ryukyus, 3422 Sesoko, Motobu, 905-0227 Okinawa, Japan,



Tuesday 24 May 2016
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